1. Field of the Invention
This invention is generally related to antigenic or immunogenic compositions and use thereof for immunization of non-human mammals, e.g. horses, against Streptococcus equi. 
2. Background of the Invention
Streptococcal infections in horses are mainly caused by the species Streptococcus equi, which is classified as a Lancefield Group C Streptococcus and comprises two subspecies designated equi and zooepidemicus, respectively.
Streptococcus equi subsp. equi, which is virtually confined to horses, is the causative agent of strangles, a world-wide distributed and highly contagious serious disease of the upper respiratory tract of the Equidae. Strangles is one of the most frequently reported equine diseases world-wide and is characterized by fever, nasal discharge, and abscess formation in the retropharyngeal and mandibular lymph nodes. In some cases the disease shows a metastatic course in the body, so called “bastard strangles”. The disease has a world-wide distribution and causes great economic losses. Moreover, since strangles is a highly contagious disease, not only infected animals but also all other members of e.g. an afflicted stud must be isolated for as long as up to three months.
S. equi subsp. zooepidemicus is considered as an opportunistic commensal often occurring in the upper respiratory tract of healthy horses. However, after stress or virus infection, it can cause a secondary infection, which results in strangles-like symptoms. Moreover, subsp. zooepidemicus infects not only horses but also a wide range of other animals, like pigs, dogs, cats, and cows. Even human cases of infection due to subsp. zooepidemicus have been reported. This subspecies has been implicated as the primary pathogen in conditions such as endometritis, cervicitis, abortion, mastitis, pneumonia, abscesses and joint infections.
Although it is possible to treat and cure these streptococcal infections with antibiotics, such as penicillin, tetracycline or gentamicin, an effective prophylactic agent that could prevent outbursts of such infections and obviate or reduce the risk for development of resistant strains associated with antibiotic treatment, would be appreciated.
3. Description of the Related Art
However, although many attempts have been made to develop prophylactic agents such as vaccines against S. equi, at the present time no efficient vaccines or immunizing preparations are available, neither for the subspecies equi nor for the subspecies zooepidemicus. 
Existing vaccines against strangles are based on inactivated, e.g. heat-killed, or attenuated strains of S. equi subsp. equi or acid extracts/mutanolysin enriched in M-protein(s), i.e. immunogenic protein(s) produced by S. equi. A vaccine against S. equi subsp, zooepidemicus based on an M-like protein is disclosed in U.S. Pat. No. 5,583,014. In WO 87/00436, an avirulent strain of S. equi is disclosed for use as a vaccine against S. equi that stimulates an antibody response in the nasopharyngeal mucosa after administration thereof to a horse.
Recently, a commercial vaccine against strangles, Equilis StrepE from IntervetVET, UK, has been released in Great Britain (November 2004), which vaccine also has been used throughout Europe and in South Africa and South America. However, the safety and efficacy of this vaccine, which is based on an attenuated (living, deletion mutated) strain of S. equi subsp. equi, can be questioned.
Since the previously developed vaccines or immunizing preparations are hampered by side-effects and, moreover, provide insufficient protection, there is a need for efficient and safe prophylactic agents, such as vaccines, that protect against S. equi infections and/or prevent spread thereof without giving rise to undesirable side-effects.
It is well known that attachment to eukaryotic cell surfaces is an essential step in the establishment of infection and colonization by bacterial pathogens. Accordingly, streptococcal surface proteins, that interact with and/or bind to different components of the Extracellular Matrix (ECM) or plasma proteins of the host cell, are potential candidates for use as active component(s) for immunizing purposes.
This is illustrated by the vaccines based on M-like proteins mentioned above or disclosed in the literature, i.a. in WO 98/01561. The binding of fibrinogen and complement factor H to M-proteins is assumed to be important for the ability of streptococci to resist phagocytosis.
Another mechanism used by streptococci for attachment to host cells involves binding to the ECM component fibronectin (Fn) (Ref. 21, 22). Binding between Fn-binding bacterial cell-surface proteins and immobilized Fn promotes internalization of streptococci by epithelial cells (Ref. 2, 23, 24). Fibronectin is a dimeric glycoprotein found both in plasma and in a fibrillar form in the extracellular matrix. The main function of Fn is to mediate substrate adhesion of eukaryotic cells, which involves the binding of specific cell-surface receptors to certain domains of the Fn molecule. Furthermore, it also interacts with several other macromolecules, such as DNA, heparin, fibrin, and collagen.
Accordingly, Fn-binding proteins from different streptococcal species have been cloned and sequenced previously. For instance, from S. equi, one Fn-binding protein has been cloned and characterized, which is a Fn-binding cell-surface protein of subsp. zooepidemicus, that has been designated FNZ (Lindmark et al., 1996, Ref. 9). Another Fn-binding protein from S. equi subsp. equi, has been cloned and characterized by Lindmark and Guss (1999) (Ref. 12). This latter protein that is designated SFS and its potential use as an active component in a vaccine for protection of horses against strangles are disclosed in WO 00/37496.
In Jonsson et al. (1995) (Ref, 8), a protein designated ZAG has been cloned and characterized from S. equi subsp. zooepidemicus that mediates binding to the plasma proteinase inhibitor α2M. It is speculated therein that this protein is similar in function to streptococcal M proteins. This protein, ZAG, is also disclosed in WO 95/07296, where its α2M-binding properties are indicated. However, immunogenic properties or potential use thereof as an active component in a vaccine for protection of e.g. horses against strangles are not disclosed therein. The gene zag encoding ZAG is also disclosed in these references.
A gene that is similar to the aforesaid zag gene from S. equi subsp. zooepidemicus but is present in subsp. equi has been described by Lindmark et al. (1999) (Ref. 11) and Lindmark (1999) (Ref. 13). This gene is hereafter designated eag and encodes a protein designated EAG.
In WO 2004/032957 A1, antigenic compositions are disclosed which comprise at least one antigen derived from a protein designated EAG, which protein is present in S. equi, and which composition suitably comprises at least one further antigen selected from a group of proteins which are present in S. equi and are, designated FNZ, SFS, SEC and SclC, respectively.
In WO 2007/115059 A2, subunit immunogenic or vaccine compositions are disclosed which comprise at least one polypeptide of S. equi having a specific amino acid sequence as shown in the sequence listing attached to said publication or an analog thereof or a fragment thereof which is a part of said polypeptide and contains at least one epitope. However, no results as regards immunizing of horses against strangles are provided in this document.
In the study reported in Lannergård, J., Frykberg, L. and Guss, B. (2003) FEMS Microbiol Lett 222: 69-74, (Ref. 28), a new gene designated one has been isolated and the corresponding protein CNE has been characterized.
In Flock, M., Jacobsson, K., Frykberg, L., Hirst, T., R., Franklin, A., Guss, B. and Flock, J.-I. (2004) Infect Immun 72:3228-3236 (Ref. 5), it is reported that in a mouse model of equine strangles, parts of the proteins designated FNZ, SFS and EAG, respectively, were used to immunize mice. FNZ and EAG were considered as promising candidates for development of a safe and efficacious vaccine against strangles.
In Lannergård, J. and Guss, B. (2006) FEMS Microbiol Lett 262: 230-235, (Ref. 26), two new proteins, IdeE and IdeZ, from S. equi subspecies equi and zooepidemicus, respectively, have been characterized as regards enzymatic activities.
In Vaccine (Timoney et al.; 2007) it is reported that a great number of recombinant extracellular proteins of S. equi, including CNE (also designated SEC) and Se 44.2 (also designated IdeE2) are useless as vaccine components. It is speculated therein that earlier results for SEC/CNE obtained for mice are not applicable to horses. Thus, it is not obvious that recombinant forms of surface localized proteins necessarily are likely candidates for vaccine components.
In Waller, A., Flock, M., Smith, K., Robinson, C., Mitchell, Z., Karlström, A., Lannergård, J., Bergman, R., Guss, B. and Flock, J.-I. (2007) Vaccine 25: 3629-3635, (Ref. 27), vaccination of horses against strangles using the recombinant antigens EAG, CNE and SclC from S. equi subspecies equi is reported. In this study, vaccinated horses showed, after challenge with S. equi subspecies equi, significantly reduced recovery of bacteria and significantly lower levels of nasal discharge.
Although many efforts have been made to develop efficient vaccines and some of the immunizing components of WO 2004/032957 A1 are promising candidates for use in a vaccine that protects against S. equi infection, development of safe vaccines having a high degree of immunogenicity and exhibiting limited or no side effects is still desirable.